1. Technical Field
The disclosed subject matter relates to a surface mounting LED substrate and LED. More particularly, it relates to a surface mounting LED plate provided with means for preventing a burr from developing at a section of a conductor pattern contained in a substrate. A burr will sometimes develop when the LED substrate is cut with a dicing blade in a dicing step, which is one of the process steps for manufacturing a surface mounting LED.
2. Description of the Related Art
A surface mounting LED can be fabricated through the process outlined below. On a multi-faced substrate having conductor patterns formed on a surface thereof, multiple LED chips are die-bonded at a certain interval with an electrically conductive adhesive interposed therebetween. Further, wire bonding is applied to the die-bonded LED chips through the use of bonding wires. Thereafter, the LED chips and the bonding wires are covered and sealed in a sealing resin.
As a result, multiple surface mounting LEDs integrated with the substrate and the sealing resin and which are multi-faced are formed on the multi-faced substrate. A dicing blade is then used to simultaneously dice the substrate and the sealing resin at a certain interval to complete the discrete surface mounting LEDs.
The surface mounting LEDs that are completed through the above process steps have some problems and some areas for improvement. One such problem is made apparent when dicing the multi-faced substrate, due to the structure of the substrate.
The general structure of a substrate used in a typical surface mounting LED will now be described. An available base material serving as a base of the substrate may include an insulator, such as paper phenol, paper epoxy, glass epoxy and ceramic, and a metal, such as aluminum and iron. A copper foil is attached onto one or both surfaces of the base material and then undesired portions are removed from the copper foil by etching to leave desired portions to form conductor patterns that are composed of the copper foil.
In typical cases, copper, nickel and gold plating may be applied in turn onto the conductor pattern, as necessary. In particular, when wire bonding is applied to connect electrodes on the LED chips with the conductor patterns via bonding wires, plating is an effective means to reliably connect the bonding wires with both electrodes.
The multiple surface mounting LEDs formed on the multi-faced substrate as described above are diced with a dicing blade of a dicer. In this case, when the conductor pattern formed on the substrate is cut with the dicing blade, a burr may develop at a section of the conductor pattern.
When the surface mounting LEDs are mounted on a motherboard, the burr may protrude downward from the surface mounting LED and prevent the LED from keeping flat relative to the motherboard. As a result, the surface mounting LEDs are mounted in random directions and/or orientations, which can result in a lack of ability to be reliably reproduced and uniformly mounted.
As a result, the surface mounting LEDs mounted on the motherboard can not satisfy various optical properties required for the surface mounting LEDs and may not be reliably mounted. This is sometimes a factor in causing a reduction in yield due to a performance failure of the motherboard.
In order to suppress development of burrs or to eliminate development of burrs at the section of the conductor pattern when dicing the substrate, the following methods have been previously undertaken or proposed.
In the former case, a generally available method comprises die bonding and wire bonding a plurality of LED chips 50 with bonding wires 51 as shown in FIG. 9A. The LED chips 50 and the bonding wires 51 are then sealed in a sealing resin 52 that is composed of a light transmissive resin to form a multi-faced substrate 53, which is set on a soft organic dicing sheet 54. A multi-faced surface mounting LED 60 that is movable with the organic dicing sheet 54 is directed to a dicing procedure in which the sealing resin 52 and the substrate 53 are simultaneously diced with a rotating dicing blade 55 from the sealing resin 52 toward the substrate 53.
This dicing method may not prevent a burr 58 from developing at a section of a conductor pattern 57 and extending downward from the substrate 53 because the dicing sheet 54 is soft. Accordingly, this method may not effectively suppress development of burrs.
As shown in FIG. 9B, the upper surface of the sealing resin 52 is set on the soft organic dicing sheet 54 in another conventional operation. Then, the multi-faced surface mounting LED 60 that is attached/movable with the organic dicing sheet 54 is directed to a dicing operation in which the substrate 53 and the sealing resin 52 are simultaneously diced with the rotating dicing blade 55 from the substrate 53 toward the sealing resin 52.
This dicing method is possible to reduce the volume of a burr 58 that may develop at the section of the conductor pattern 57 and which extends downward from the substrate 53. In this orientation, however, the appearance of products can not be inspected and the sealing resin 52 set may possibly be peeled off on dicing under pressure and vibrations from the dicing blade 55.
Further, in another conventional operation shown in FIG. 9C, the multi-faced substrate 53 is adhered on an almost flat surface of a plate of ice 56. Then, the multi-faced surface mounting LED 60 is moved with the almost flat ice 56 and directed to a dicing operation in which the sealing resin 52 and the substrate 53 are simultaneously diced with the dicing blade 55 rotating in a direction from the sealing resin 52 toward the substrate 53.
This dicing method makes it possible to prevent a burr 58 from developing at the section of the conductor pattern 57 and extending downward from the substrate 53 because the lower surface of the substrate 53 makes contact with a hard member (ice 56). This method, however, requires time for adhering (fixing) the substrate on the almost flat surface of the ice 56 and is difficult for use in mass production.
On the other hand, a method that allows no development of burrs during a dicing operation is shown in FIG. 10. This method involves the specific formation of the conductor pattern 57 on the lower surface of the substrate 53, which are the most troublesome portion of the conductor pattern associated with development of burrs. Portions of the conductor pattern located at least on a dicing line 59 are removed to allow dicing without cutting the conductor pattern. Japanese Patent publication JP-A 2002-222997 is a conventional art example of such a dicing method.
The method shown in FIG. 10 requires that a portion of the conductor pattern be removed, the removed portion having a width larger than the dicing width (the thickness of the dicing blade). As a result, the area of the conductor pattern formed on the lower surface of the substrate for the surface mounting LED is reduced and lowers the strength of the product against stress. In addition, when the product is mounted on a motherboard with an electrically conductive member interposed therebetween, the small area of the conductor pattern serving as a bonding electrode on the product results in a reduction in fixing force against a lateral weight.